Cytomegalovirus is the leading infectious cause of birth defects which can result in deafness and mental retardation in neonates, and can cause severe viral pneumonia and colitis in transplant recipients and sight-threatening retinitis in patients with AIDS. Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with a number of cancers including Burkitt lymphoma, nasopharyngeal carcinoma, Hodgkin lymphoma, and post-transplant lymphoproliferative disease. Human CMV and EBV naturally infect humans, but not small animals or nonhuman primates. The best models currently available for CMV and EBV are rhesus monkey CMV and EBV. The goal of this study is to develop an effective vaccine for these rhesus viruses and to use these as a model for vaccines for their human counterparts. We are using various approaches including soluble recombinant proteins, virus-like particles, recombinant virus vectors expressing viral proteins, and replication defective viruses as vaccines. We have been using an animal model, rhesus monkey EBV in rhesus macaques, to compare various candidate EBV vaccines. Rhesus EBV causes a similar disease in monkeys as EBV does in humans and the viruses have the same number of virus genes that have virtually the same activities. We are currently comparing vaccines to different combinations of rhesus EBV glycoproteins. We have vaccinated the animals and recently challenged them to try to determine which glycoproteins are most important for protection from infection. We have also developed a candidate vaccine virus for rhesus CMV in which we deleted a protein from the virus that is essential for virus growth. The resulting replication-defective virus lacks one viral protein, glycoprotein L (gL), and replicates only in cells expressing rhesus CMV gL. In addition, noncomplementing cells infected with the replication-defective rhesus CMV produced glycoprotein B, the major target of neutralizing antibodies, at levels similar to those observed in cells infected with wild-type virus. We are testing this candidate vaccine in rhesus monkeys. The prototype strain of rhesus CMV is termed 68-1. This strain has been used in studies of pathogenesis and vaccine development. We determined the complete sequence of a region of rhesus CMV 68-1 which includes several proteins important for host cell tropism, directly from the origin urine from which the virus was isolated in 1968. We compared the sequence of the unpassaged rhesus CMV 68-1 virus with laboratory passaged virus currently in use in the United States. The sequence of laboratory passaged virus shows insertions, deletions, and stop codons in several genes compared with the unpassaged isolate. Virus genes important for cellular tropism and for immune evasion were the most common sites of mutations in laboratory isolates of the virus.